I'd put the chances of a Serenity sequel happening has having moved up a bit. Granted through no actual means of it's own merit but still, I'd place it back into the wait and see category.

I'd say the chances are still pretty slim for a Serenity sequel. Even if some bean counter decided to take another gamble and greenlit it, there's a good possibly they couldn't get all the cast. Hell, Nathan Fillion currently has a popular show he's committed to.